Multi-power domain operational amplifier and voltage generator using the same

ABSTRACT

A multi-power domain operational amplifier includes an input stage circuit, a power domain transforming circuit and an active load. The input stage circuit is configured to transform a set of input voltages into a set of input currents in a first power domain. The power domain transforming circuit is configured to transform the set of input currents into a set of output currents in a second power domain. The active load is configured to generate an output voltage according to the set of output currents. A common mode range of the output voltage is shifted as compared with a common mode range of the set of input voltages.

This application claims the benefit of Taiwan application Serial No.101106411, filed Feb. 24, 2012, the subject matter of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a multi-power domain operational amplifier anda voltage generator using the same.

2. Description of the Related Art

Because of the properties of semiconductor elements, many applicationsneed a set of a positive reference voltage and a negative referencevoltage, which are not affected by the temperature and are about +5volts and −5 volts, respectively. The +5 volts and −5 volts approach thevoltage withstanding upper bound (6 volts) of the medium voltageelement. In the industry, a bandgap reference circuit is typicallyutilized to generate a zero temperature coefficient reference voltage ofabout 1.2 volts, and boost and buck operations are performed through aregulator based on the zero temperature coefficient reference voltage.Thus, various reference voltages for various applications can begenerated.

FIG. 1 is a circuit diagram showing an example of a conventional voltagegenerator 10. Referring to FIG. 1, the voltage generator 10 includes aunity gain buffer 12, a first regulator 14 and a second regulator 16. InFIG. 1, the operation voltage VDD is equal to 3 volts, for example, andthe zero temperature coefficient reference voltage V_(ref) generated bythe bandgap reference circuit is equal to 1.2 volts, for example. Boostand buck operations may be performed on the zero temperature coefficientreference voltage V_(ref) by utilizing the first regulator 14 and thesecond regulator 16 according to the resistance relationship:(R1+R2)/R1=5/1.2 so that the positive reference voltage V_(outP)=5 voltsand the negative reference voltage V_(outN)=−5 volts can be obtained.Because the second regulator 16 takes the ground voltage (0 volts) asthe reference point, the power domain of its internal operationaltransductance amplifier (OTA) 18 needs to range from VDD to −2 VDD(i.e., from 3 volts to −6 volts), which exceeds the voltage withstandingrestriction of the medium voltage element. So, the high voltage elementhas to be adopted. Consequently, the poor element property of the highvoltage element reduces the overall circuit behavior, and occupies a lotof layout area.

FIG. 2 is a circuit diagram showing another example of a conventionalvoltage generator 20. Referring to FIG. 2, the voltage generator 20includes a unity gain buffer 22, a first regulator 24, a secondregulator 26 and a third regulator 28. In FIG. 2, the operation voltageVDD is equal to 3 volts, for example, and the zero temperaturecoefficient reference voltage V_(ref) generated by the bandgap referencecircuit is equal to 1.2 volts, for example. The zero temperaturecoefficient reference voltage V_(ref) utilizes the first regulator 24 toperform a boosting operation according to the resistance relationshipand thus obtain the positive reference voltage V_(outP)=5 volts. Inaddition, the zero temperature coefficient reference voltage V_(ref)utilizes the second regulator 26 to perform a bucking operation with theground voltage (0 volts) serving as the reference point to obtain−V_(ref)=1.2 volts first, and then utilizes the third regulator 28 toperform two bucking operations to obtain the negative reference voltageV_(outN)−5 volts. With the cascaded two stages of regulator structures26 and 28, the power domain of the second regulator 26 ranges from VDDto −VDD (i.e., from 3 volts to −3 volts), and the power domain of thethird regulator 28 ranges from GND to −2 VDD (i.e., from 0 volts to −6volts), wherein the power domains are kept within the voltagewithstanding range of the medium voltage element and the use of the highvoltage element can be avoided. In the structure of the voltagegenerator 20, however, an additional stage of regulators may make theoutput voltage have an offset and be affected by the power noise.

In addition, in the process of transforming the positive voltage intothe negative voltage, the voltage generators 10 and 20 need to use theunity gain buffers 12 and 22, respectively, so that the zero temperaturecoefficient reference voltage V_(ref) possesses the driving ability toprovide the current output. However, using the unity gain buffers 12 and22 increases the circuit complexity and the layout area, and alsoincreases the offset of the output voltage and the influence of thepower noise.

SUMMARY OF THE INVENTION

The disclosure is directed to a multi-power domain operational amplifierand a voltage generator using the same. The transformation of the powerdomain of the multi-power domain operational amplifier enables thevoltage generator to generate the required positive reference voltageand negative reference voltage without using the high voltage element.

According to a first aspect of the disclosure, a multi-power domainoperational amplifier including an input stage circuit, a power domaintransforming circuit and an active load is provided. The input stagecircuit is configured to transform a set of input voltages into a set ofinput currents in a first power domain. The power domain transformingcircuit is configured to transform the set of input currents into a setof output currents in a second power domain different from the firstpower domain. The active load is configured to generate an outputvoltage according to the set of output currents, wherein a common moderange of the output voltage is shifted as compared with a common moderange of the set of input voltages.

According to a second aspect of the disclosure, a voltage generatorincluding a cascade resistor, a first regulator and a second regulatoris provided. The cascade resistor has a first feedback terminal and asecond feedback terminal. The first regulator is configured to output afirst output voltage, and includes a multi-power domain operationalamplifier having a negative feedback configuration. The multi-powerdomain operational amplifier operates in a first power domain and asecond power domain different from the first power domain and has aninverting input terminal receiving a first reference voltage, and anoninverting input terminal coupled to the first feedback terminal. Thesecond regulator is configured to output a second output voltage andincludes a single power domain operational amplifier operating in athird power domain and having the negative feedback configuration. Thesingle power domain operational amplifier has an inverting inputterminal receiving a second reference voltage, and a noninverting inputterminal coupled to the second feedback terminal.

The above and other aspects of the invention will become betterunderstood with regard to the following detailed description of thepreferred but non-limiting embodiment(s). The following description ismade with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an example of a conventional voltagegenerator.

FIG. 2 is a circuit diagram showing another example of a conventionalvoltage generator.

FIG. 3 is a schematic illustration showing a multi-power domainoperational amplifier according to an embodiment.

FIG. 4 is a circuit diagram showing a multi-power domain operationalamplifier according to an embodiment.

FIG. 5 is a circuit diagram showing a multi-power domain operationalamplifier according to another embodiment.

FIG. 6 is a circuit diagram showing a voltage generator according to anembodiment.

DETAILED DESCRIPTION OF THE INVENTION

This disclosure provides a multi-power domain operational amplifier anda voltage generator using the same. The transformation of the powerdomain regulates the common mode range of the multi-power domainoperational amplifier, so that the voltage generator can generate therequired positive reference voltage and negative reference voltagewithout using high voltage elements. Words utilized for describingconnection between two components such as “couple” and “connect” shouldnot be taken as limiting a connection between the two components todirectly coupling or indirectly coupling.

FIG. 3 is a schematic illustration showing a multi-power domainoperational amplifier 300 according to an embodiment. Referring to FIG.3, the multi-power domain operational amplifier 300 includes an inputstage circuit 310, a power domain transforming circuit 320 and an activeload 330. The input stage circuit 310 is coupled to a first voltagesource VDD, which may be composed of a single PMOS input pair and asingle NMOS input pair or composed of a PMOS input pair and an NMOSinput pair. The input stage circuit 310 is configured to transform a setof input voltages (V_(in+), V_(in−)) into a set of input currents(I_(in+), I_(in−)) in a first power domain. The first power domainranges between the first voltage source and the second voltage source.In this example, the first voltage source is VDD while the secondvoltage source is −VDD. That is, the first power domain is (from VDD to−VDD). Specifically, the first voltage source VDD is 3 volts, while thesecond voltage source −VDD is −3 volts, for example.

The power domain transforming circuit 320 includes a first currentbuffer and a second current buffer. The first current buffer is coupledbetween the input stage circuit 310 and the second voltage source −VDD,and is configured to transform the set of input currents (I_(in+),I_(in−)) into a set of relay currents in a relay power domain. The firstrelay power domain ranges between the second voltage source and thethird voltage source (e.g., GND). In this example, the first relay powerdomain is (−VDD to GND). The second current buffer is coupled betweenthe first current buffer and the third voltage source GND, and isconfigured to generate a set of output currents (I_(out+), I_(out−)) ina second power domain according to the set of relay currents. The secondpower domain ranges between the third voltage source and a fourthvoltage source (e.g., −2 VDD). In this example, the second power domainis (GND to −2 VDD) (more specifically, from 0 volts to −6 volts).

The active load 330 may be composed of a current mirror or a currentsource, is coupled between the second current buffer and the fourthvoltage source −2 VDD, and is configured to generate an output voltageV_(out) according to the set of output currents (I_(out+), I_(out−)). Acommon mode range (from GND to −2 VDD) of the output voltage V_(out) isshifted as compared with a common mode range (from VDD to −VDD) of theset of input voltages (V_(in+), V_(in−)).

FIG. 4 is a circuit diagram showing a multi-power domain operationalamplifier 400 according to an embodiment. Referring to FIG. 4, themulti-power domain operational amplifier 400 includes an input stagecircuit 410, a power domain transforming circuit 420 and an active load430. The input stage circuit 410 may be composed of a PMOS input pair,and is coupled to the first voltage source VDD. The input stage circuit410 transforms the input voltages (V_(in+), V_(in−)) into the inputcurrents (I_(in+), I_(in−)). In the example of FIG. 4, the power domaintransforming circuit 420 is a current mirror circuit. The current mirrorcircuit 420 has a first current mirror 422 and a second current mirror424 implementing the first current buffer and the second current buffer,respectively.

The first current mirror 422 is coupled between the input stage circuit410 and the second voltage source −VDD, and is configured to transformthe input currents (I_(in+), I_(in−)) into the relay currents (I_(re+),I_(re−)). The second current mirror 424 is coupled between the firstcurrent mirror 422 and the third voltage source GND, and is configuredto provide the output currents (I_(out+), I_(out−)) to the active load430 according to the third voltage source GND serving as the referencepoint so that the output voltage V_(out) is generated. The active load430 is coupled between the second current mirror 424 and the fourthvoltage source −2 VDD. Because the common mode range of the outputvoltage V_(out) is shifted as compared with the common mode range of theinput voltages (V_(in+), V_(in−)), the voltage from GND to −2VDD (e.g.,from 0 volts to −6 volts) can be outputted with the GND=0 volts servingas the reference point without using the high voltage element.

FIG. 5 is a circuit diagram showing a multi-power domain operationalamplifier 500 according to another embodiment. Referring to FIG. 5, themulti-power domain operational amplifier 500 includes an input stagecircuit 510, a power domain transforming circuit 520 and an active load530. The input stage circuit 510 is composed of a PMOS input paircoupled to the first voltage source VDD. The input stage circuit 510transforms the input voltages (V_(in+), V_(in−)) into the input currents(I_(in+), I_(in−)). In the example of FIG. 5 to be described, the powerdomain transforming circuit 520 is a folded-cascode circuit, which has afirst folded-cascode 522 and a second folded-cascode 524 forimplementing the first current buffer and the second current buffer,respectively.

The first folded-cascode 522 is coupled between the input stage circuit510 and the second voltage source −VDD, and is configured to transformthe input currents (I_(in+), I_(in−)) into the relay currents (I_(re+),I_(re−)). The second folded-cascode 524 is coupled between the firstfolded-cascode 522 and the third voltage source GND, and is configuredto provide the output currents (I_(out+), I_(out−)) to the active load530 according to the third voltage source GND serving as the referencepoint, so that the output voltage V_(out) is generated. The active load530 is coupled between the second folded-cascode 524 and the fourthvoltage source −2VDD. Because the common mode range of the outputvoltage V_(out) is shifted as compared with the common mode range of theinput voltages (V_(in+), V_(in−)), the voltage from GND to −2VDD (e.g.,from 0 volts to −6 volts) can be outputted with the GND=0 volts servingas the reference point without using the high voltage element. Inaddition, because the multi-power domain operational amplifier 500utilizes the folded cascode structure to receive and output thecurrents, it has the better linear voltage regulating andnoise-resisting ability, and can provide the higher input common moderange and output common mode range under the same power.

Although two current buffers are described as the example of the powerdomain transforming circuit 420/520, the invention is not restrictedthereto. The power domain transforming circuit 420/520 may furtherinclude one to many third cascading current buffers, which are coupledbetween the first current buffer and the second current buffer andconfigured to generate the other one to many sets of relay currentsaccording to the relay currents (I_(re+), I_(re−)) from the firstcurrent buffer or according to the relay currents from a previous stageof the cascading current buffers, and provide one of the other one tomany sets of relay currents to the second current buffer or to a nextstage of the cascading current buffers. The other one to many sets ofrelay currents have different power domains.

FIG. 6 is a circuit diagram showing a voltage generator 600 according toan embodiment. Referring to FIG. 6, the voltage generator 600 includes acascade resistor R1, a first regulator 610 and a second regulator 620.The cascade resistor R1 has a first feedback terminal (node A) and asecond feedback terminal (node B). The first regulator 610 is configuredto output a first output voltage V_(outN). The first regulator 610includes a multi-power domain operational amplifier 615 with a negativefeedback configuration, resistors R3 and R4 serially connected togetherand a transistor M1, wherein R3=R1 and R4=R2. The first terminal of theresistor R3 is coupled to the first feedback terminal (node A). Thetransistor M1 has a first terminal coupled to the voltage source −2VDD,a second terminal coupled to the second terminal of the resistor R4 anda control terminal coupled to an output terminal of the multi-powerdomain operational amplifier 615.

The actual circuit architecture of the multi-power domain operationalamplifier 615 may be shown in the multi-power domain operationalamplifier 300/400/500. The multi-power domain operational amplifier 615is coupled between a first voltage source VDD and a second voltagesource −VDD, and is coupled between a third voltage source GND and afourth voltage source −2VDD. The multi-power domain operationalamplifier 615 operates in a first power domain (from VDD to −VDD) and asecond power domain (from GND to −2VDD). The multi-power domainoperational amplifier 615 has an inverting input terminal receiving afirst reference voltage GND, and a noninverting input terminal coupledto the first feedback terminal (node A). Consequently, the firstfeedback terminal (node A) is regulated at the first reference voltageGND.

Because the first regulator 610 utilizes the multi-power domainoperational amplifier 615, the voltage from GND to −2VDD (i.e., from 0volts to −6 volts) can be generated with the first reference voltage GNDserving as the reference point without using the high voltage element.

The second regulator 620 is configured to output a second output voltageV_(outP). The second regulator 620 includes a single power domainoperational amplifier 625 operating in a third power domain (from 2 VDDto GND) and having a negative feedback configuration, a resistor R2 anda transistor M2. The first terminal of the resistor R2 is coupled to thesecond feedback terminal (node B). The transistor M2 has a firstterminal coupled to the voltage source 2 VDD, a second terminal coupledto the second terminal of the resistor R2, and a control terminalcoupled to an output terminal of the single power domain operationalamplifier 625. The single power domain operational amplifier 625 iscoupled between a fifth voltage source 2 VDD and the third voltagesource GND. The single power domain operational amplifier 625 has aninverting input terminal receiving a second reference voltage V_(ref),and a noninverting input terminal coupled to the second feedbackterminal (node B). Consequently, the second feedback terminal (node B)is regulated at the second reference voltage V_(ref).

The first regulator 610 and the second regulator 620 can be merged byproviding the current from the second feedback terminal (node B) coupledto the second regulator 620 to the first feedback terminal (node A)coupled to the first regulator 610. Consequently, the required DCcurrent flowing through the resistors R2, R3 and R4 is generated on theresistor R1 according to V_(feedback,B)=V_(ref)=1.2 volts andV_(feedback,A)=GND=0 volts, so that the first output voltage V_(outN)=−5volts and the second output voltage V_(outP)=5 volts can be obtained.

In the multi-power domain operational amplifier of the embodiment andthe voltage generator using the same, the common mode range of themulti-power domain operational amplifier can be regulated via the powerdomain transformation of the multi-power domain operational amplifier,so that the voltage generator can generate the required positivereference voltage and negative reference voltage utilizing a smallnumber of regulators without using the high voltage element.Consequently, the circuit design complexity can be simplified, thelayout area can be reduced, the voltage offset caused by the elementmismatch can be significantly decreased, and the power noise generatedthrough the power transistor can be reduced.

While the invention has been described by way of example and in terms ofthe preferred embodiment(s), it is to be understood that the inventionis not limited thereto. On the contrary, it is intended to cover variousmodifications and similar arrangements and procedures, and the scope ofthe appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

What is claimed is:
 1. A multi-power domain operational amplifier,comprising: an input stage circuit configured to transform a set ofinput voltages into a set of input currents in a first power domain; apower domain transforming circuit configured to transform the set ofinput currents into a set of output currents in a second power domaindifferent from the first power domain; and an active load configured togenerate an output voltage according to the set of output currents,wherein a common mode range of the output voltage is shifted as comparedwith a common mode range of the set of input voltages; and wherein thepower domain transforming circuit comprises cascading current bufferseach involving a different power domain.
 2. The operational amplifieraccording to claim 1, wherein the cascading current buffers of the powerdomain transforming circuit comprise: a first current buffer configuredto transform the set of input currents into a set of first relaycurrents in a first relay power domain different from the first powerdomain; and a second current buffer configured to generate the set ofoutput currents according to the set of first relay currents.
 3. Theoperational amplifier according to claim 2, wherein the input stagecircuit is coupled to a first voltage source, the first current bufferis coupled between the input stage circuit and a second voltage source,the second current buffer is coupled between the first current bufferand a third voltage source, and the active load is coupled between thesecond current buffer and a fourth voltage source.
 4. The operationalamplifier according to claim 2, wherein the cascading current buffers ofthe power domain transforming circuit further comprise: at least onethird current buffer, which is coupled between the first current bufferand the second current buffer, and is configured to generate at leastone set of second relay currents according to the set of first relaycurrents in a second relay power domain different from the first powerdomain and the first relay power domain, and to provide one of the atleast one set of second relay currents to the second current buffer. 5.The operational amplifier according to claim 1, wherein the input stagecircuit utilizes a PMOS input pair or an NMOS input pair to transformthe set of input voltages into the set of input currents.
 6. Theoperational amplifier according to claim 1, wherein the input stagecircuit utilizes a PMOS input pair and an NMOS input pair to transformthe set of input voltages into the set of input currents.
 7. Theoperational amplifier according to claim 1, wherein the power domaintransforming circuit is a current mirror circuit.
 8. The operationalamplifier according to claim 7, wherein the input stage circuit iscoupled to a first voltage source, the current mirror circuit has afirst current mirror coupled between the input stage circuit and asecond voltage source, and a second current mirror coupled between thefirst current mirror and a third voltage source, and the active load iscoupled between the second current mirror and a fourth voltage source.9. The operational amplifier according to claim 1, wherein the powerdomain transforming circuit is a folded-cascode circuit.
 10. Theoperational amplifier according to claim 9, wherein the input stagecircuit is coupled to a first voltage source, the folded-cascode circuithas a first folded-cascode coupled between the input stage circuit and asecond voltage source, and a second folded-cascode coupled between thefirst folded-cascode and a third voltage source, and the active load iscoupled between the second folded-cascode and a fourth voltage source.11. The operational amplifier according to claim 1, wherein the activeload is composed of a current mirror or a current source.